The Planets

by Dava Sobel

(Viking, 2005, $24.95, 288 pages)

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Seeing in the Dark by Timothy Ferris, also reviewed on this site.
Most reviews tell readers about what a book is. But because Dava Sobel's new book The Planets is such a great departure from her previous best-sellers, this review begins with a discussion of what it is not.

Those earlier works reaped not only impressive sales and an appreciative readership, but also critical acclaim. Newsday called Galileo's Daughter "innovative history and a wonderfully told tale." The Washington Post praised Longitude as "a simple tale, brilliantly told, and the New York Times raved, "Sobel is a master storyteller."

Indeed, the appeal of both of those books is similar to that of well-crafted novels. They have remarkable central characters, strong and appealing supporting casts, fascinating questions that hook readers immediately, well-drawn narratives to carry them through the story, and subplots to add depth and texture.

Readers looking for that kind of story telling and in-depth information will be disappointed by The Planets, for this time Sobel intended to write a very different book. It is part memoir, part anthology, part short-story collection, part anecdotal gossip, and part reverie.

Its opening words invite the readers to connect with own their childhood discoveries that Earth was not the center of the Universe. "My planet fetish began, as best I can recall, in third grade, at age eight--right around the time I learned the Earth had siblings in space, just as I had older brothers in high school and college."

Sobel goes on to describe her attempt to create a model of the Solar System, a "crude diorama, produced with a complete lack of artistic skill," including neither Sun nor Moon but nevertheless capturing the family of bodies that make up our neighborhood in space. That, combined with Sobel's stories of a school planet play and a class trip to the Hayden Planetarium, announces to her audience that this book is her history--and theirs.

She then crafts a new Solar System diorama in words, this time including not only the Sun and Earth's Moon as major pieces of the model but also glimpses of the moons of other planets, bodies beyond Pluto, planetary systems beyond our own, and the vast sea of galaxies in which our Milky Way is but a speck.

Beginning with the Sun and working outward, each chapter portrays its featured heavenly body according to a distinct theme. For the Sun, the theme is Genesis. It was born in the collapse of a slowly rotating thin cloud of hydrogen and helium gases sprinkled with stardust. The debris that event left behind became the rest of the book's family of worlds.

Mercury's theme is Mythology and Venus' is Beauty. Earth's is Geography, where echoes of Longitude appear. Then comes the Moon's Lunacy and the sci-fi visions of Mars.

Sobel's literary relationship with Galileo--besides Galileo's Daughter, she also translated and edited a collection of that daughter's correspondence called Letters to Father--dominates the chapter on Jupiter. She tells the life stories not only of the Italian scientist but also the spacecraft of the same name. That heroic craft observed the giant planet and its moons for several years before scientists sent it on a final suicide mission into Jupiter's clouds in 2003.

That chapter will rankle many readers. Its theme is Astrology, a field that is rooted in the same historical observations as Astronomy but has turned to mysticism rather than science.

In this period of antiscientific discourse among many political and educational policy-makers, scientifically inclined readers will cringe when Sobel's prose gives credence to the casting of horoscopes for both Galileos: the scientist who discovered Jupiter's four largest moons, and the exemplary piece of modern technology that explored the entire Jovian system.

Saturn's theme is "Music of the Spheres," which includes a discussion of Gustav Holst's The Planets plus an overview of the complex system of bodies in orbit around it, including giant moons and tiny fragments orbiting in rings resembling the grooves on a phonograph record.

Then it's onward to "Discovery" and the near-twin ice giants Uranus and Neptune. William Herschel was the first to recognize Uranus as a planet in 1781, though others had occasionally noted it years earlier as an unknown star on their charts. The keenest observers could see it with their naked eyes on the darkest of nights, but its true identity as a planet required telescopic observations of its position over several days.

Despite Uranus' slow progression across the sky--its orbital period is 84 years--the earlier observations made it possible for astronomers to compute its orbit. By the late 1820s, the accumulation of measurements clearly revealed a deviation of that orbit from the path predicted by Newton's law of gravity. The most likely cause was another planet still farther from the Sun.

In a remarkable feat of mathematics, two astronomers on opposite sides of the English Channel independently predicted where that planet could be seen. In England, a young astronomer named Adams completed his calculation nearly a year before the accomplished French scientist, M. Leverrier, but the British Astronomer Royal withheld Adams work until after Leverrier had published, and it was Leverrier's 1845 prediction that led almost immediately to Neptune's discovery.

That account is the most detailed in the book--nearly twenty pages--and is closest to the vivid story-telling technique of Sobel's earlier books. She describes the discoveries and the culture of science in the 97-year-old voice of William Herschel's closest colleague and sister, Caroline Herschel. Most of the chapter takes the form of an imagined letter written in 1847 to the much younger but already distinguished woman astronomer Maria Mitchell. The letter is remarkably convincing. Readers who skip the "Details" section of the back matter may not recognize that it is, in fact, the author's invention.

The theme for Pluto is "UFO," appropriate because the planetary status of that distant, icy world is in dispute. Sobel uses that uncertain status as a way to introduce the outermost objects in the Solar System. She also uses it to take leave of her readers with open questions dangling.

In a brief epilogue, Sobel heads out for a summer 2004 party of "Planeteers" celebrating the successful insertion of the Cassini spacecraft into orbit around Saturn. Their models of the Solar System may be more sophisticated than hers, but they are still incomplete. They will refine those models with scientific results from Cassini and the Huygens probe that will land on Titan, the planet's largest moon, six months later. But that night they celebrate the loose ends and drink toasts to the questions that they do not know yet to ask.